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This is not a full answer, I would just like to share the knowledge I obtained by studying two of the papers mentioned in the question: Steerable Importance Sampling and Practical Product Importance Sampling for Direct Illumination. Steerable Importance Sampling In this paper they propose a method for sampling the product of the clamped cosine component ...

4

Disclaimer: I have no idea what is the state of the art in the environmental map sampling. In fact, I have very little knowledge about this topic. So this will not be complete answer but I will formulate the problem mathematically and analyze it. I do this mainly for myself, so I make it clear for my self but I hope that OP and others will find it useful. ...

4

Yes, you do need to transform the fetch direction into the space of the cubemap. If you could somehow figure out the fetch direction in the vertex shader, then you could do the transformation there instead, but that would produce worse lighting. It also may be worth optimizing for a smaller number of interpolants between the vertex and pixel shaders (rather ...

3

1)What is the V vector? How did they compute that It's the vector toward the camera (view vector), i.e. direction of the reflected ray. The lookup table they're building is parameterized in terms of NdotV, so they are working backward from NdotV to obtain a corresponding V vector. For purposes of doing this integration it doesn't matter what N and V are ...

2

How are you randomizing the samples you take? It looks to me like maybe the random values are the same across all pixels in the image, which would explain why you see 10 coherent bright spots when you have 10 samples. The samples should be re-randomized for each pixel. This should produce a noisy result, with a single blurred-out bright spot instead of 10 (...

2

There's two main things it seems like you've not understood correctly. IBL is for indoor scenes and outdoor scenes In the early days when IBL was hot, the Uffizi light-probe was probably the most popular for researchers. IBL works really well for indoor scenes with strong light coming from multiple directions, such as churches with stained glass. That kind ...

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Think of this way: when integrating uniformly over the hemisphere, it's like you are importance-sampling with a constant pdf of $1/2\pi$. The multiplication by $2\pi$ at the end, then, can be seen as the division by the pdf, factored out of the sum because it's constant. The constant pdf is $1/2\pi$ (as opposed to some other number) because it needs to be ...

1

I recommend to ignore my post (however I consider papers that I've sent valueable) and read post of Nathan Reed, which is much better in explaining this problem! I'm still a junior when it comes to computer graphics so you may want to take my opinion with a grain of salt: To start with - I used to learn/implement stuff using website that you've sent (OpenGL) ...

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I've actually managed to find problem thanks to @PaulHK, thanks! I decided to pass which face I am currently working on and setting then coordinates manually per face. It is awful but it works rather good and since it is prefiltered and not done in runtime I found it good enough: [branch] if (g_upVectorVal.z == 1.0f) { input.position.z = -1.0f; } [...

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